Fix comparison base for line table compression (#54032)
I'm not entirely sure what the original intent of this statement was,
but the effect ends up being that some codeloc entries end up negative
in the compressed representation, but the code always assumes unsigned
integers, so things roundtripped badly, leading to badly corrupted stack
traces. I guess this might have been a rebase mistake,
since the same line exists (correctly) a few lines prior. Fixes #54031.
